1. Field of the Invention
The present invention relates to a starter and, more particularly, to a starter which is equipped with an epicyclic reduction gear and which is used to start an engine of a vehicle.
2. Description of the Prior Art
A conventional starter used to start an engine of a vehicle has heretofore been arranged as shown in FIG. 2.
The conventional starter 1 shown in FIG. 2 has a d.c. motor 2 for generating the rotational force that is used to start an engine. An epicyclic reduction gear 3 is disposed adjacent to the forward end (that is, the right-hand end as viewed in FIG. 2) of the latter. The epicyclic reduction gear 3 comprises a sun gear 3a which is in fitting engagement with straight splines 2b formed in the outer peripheral surface of the end portion of an armature rotary shaft 2a of the motor 2, an internal gear 3b disposed around the sun gear 3a, and planet gears 3c which are meshed with both the sun gear 3a and the internal gear 3b to revolve about the sun gear 3a while rotating around their own axes. The planet gears 3a are supported on a carrier 3e through respective pins 3d.
At the forward end of the d.c. motor 2, a driving shaft 4 which is a member separate from the armature rotary shaft 2a is disposed on the same axis as the central axis of the shaft 2a. A boss-shaped tubular portion of the carrier 3e that constitutes the epicyclic reduction gear 3 is firmly fitted on the rear end of the driving shaft 4 by means of spline engagement. The internal gear 3b that also constitutes the epicyclic reduction gear 3 is formed integral with a center bracket 5. The boss-shaped tubular portion of the carrier 3b is rotatably supported through a bearing 6 which is fitted to the center bracket 5.
An overrunning clutch 7 is axially slidably supported on the driving shaft 4 at a position which is adjacent to the forward end of the center bracket 5. More specifically, the overrunning clutch 7 consists of a clutch outer member 7a and a clutch inner member 7c. The clutch outer member 7a is meshed with a helical spline 4a formed in the driving shaft 4 so that the rotation of the driving shaft 4 is transmitted to the clutch inner member 7c through rollers 7b. The clutch inner member 7c has a tubular output shaft portion 7d which is formed integral therewith and which is fitted and supported on the driving shaft 4 through a bearing 8. The outer periphery of the output shaft portion 7d is supported by a bearing 10 which is firmly fitted to a front bracket 9 defining a machine frame of the starter 1. A pinion 11 which is engageable with a ring gear (not shown) of the engine is secured to the distal end of the output shaft portion 7d.
It should be noted that the reference numeral 12 in FIG. 2 denotes an electromagnetic switch which is arranged to shift the overrunning clutch 7 at the same time as the power supply of the d.c. motor 2 is turned on. One end of a shift lever 13 is engaged with a plunger rod of the switch 12, while the other end of the shift lever 13 is engaged with a circumferential groove which is formed in the outer peripheral surface of the clutch outer member 7a of the overrunning clutch 7.
As described above, in the conventional starter, the armature rotary shaft 2a of the d.c. motor 2 is separated from the driving shaft 4, and one end of the driving shaft 4, together with the boss-shaped tubular portion of the carrier 3e, is supported through the bearing 6 which is fitted to the center bracket 5 formed integral with the internal gear 3b of the epicyclic reduction gear 3. Hence, the prior art suffers from the problem that the overall length of the starter is disadvantageously long.